Stainless Steel Coil Tube (Coiltube) — Series 794
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Category: Formed Tubular Products — Coil / Spiral Tubing
Reference Document: Analysis of Fan Coil Unit (FCU) Applications in Practical Engineering Projects
1. Product Overview
The Series 794 Stainless Steel Coil Tube is a precision-formed tubular product engineered for thermal exchange, fluid conveyance, and structural applications within mechanical and HVAC (Heating, Ventilation, and Air Conditioning) systems. Unlike straight-length stainless steel tubing, the coil tube is supplied in continuous helical or spiral configurations, offering significant advantages in material utilization, on-site installation flexibility, and reduction of field welding points.
This product line draws upon extensive engineering experience in the deployment of Fan Coil Units (FCUs) in commercial and industrial buildings. In FCU applications, stainless steel coil tubes serve as the primary heat transfer elements within evaporator and condenser coils, where they are exposed to condensate, refrigerants, and ambient moisture. The selection of stainless steel over carbon steel or copper-alloy tubing addresses critical concerns regarding corrosion resistance, long-term durability, and hygienic performance in high-humidity environments.
2. Material Composition & Properties
The coil tubes are manufactured from austenitic stainless steel grades conforming to internationally recognized metallurgical standards. The primary grade employed is ASTM A213 TP304 / TP316L, with grade selection governed by the specific service environment.
- Grade 304 (UNS S30408): Suitable for general-purpose HVAC and water handling applications. Contains approximately 18–20% Chromium (Cr) and 8–10% Nickel (Ni), providing robust resistance to atmospheric and freshwater corrosion.
- Grade 316L (UNS S31603): Recommended for aggressive environments involving chlorides, condensate with high dissolved salt content, or marine-adjacent installations. The addition of 2–3% Molybdenum (Mo) significantly enhances pitting and crevice corrosion resistance.
Key mechanical and thermal properties are summarized below:
| Property | Grade 304 | Grade 316L |
|---|---|---|
| Yield Strength (0.2% Offset) | ≥ 205 MPa (29.7 ksi) | ≥ 170 MPa (24.7 ksi) |
| Tensile Strength (UTS) | 515–725 MPa (75–105 ksi) | 485–725 MPa (70–105 ksi) |
| Elongation at Fracture | ≥ 40% | ≥ 40% |
| Thermal Conductivity (at 25°C) | 16.3 W/(m·K) | 14.6 W/(m·K) |
| Thermal Expansion Coefficient (20–100°C) | 17.3 × 10⁻⁶ /°C | 16.8 × 10⁻⁶ /°C |
| Operating Temperature Range | −196°C to +870°C | −196°C to +870°C |
| Maximum Service Pressure (Schedule 40S, 1/2" OD) | ≥ 16 bar (232 psi) | ≥ 16 bar (232 psi) |
3. Technical Specifications
| Parameter | Specification |
|---|---|
| Product Designation | Series 794 Stainless Steel Coil Tube |
| Outer Diameter (OD) Range | 6.35 mm (1/4") to 50.8 mm (2") |
| Wall Thickness Range | 0.50 mm to 3.00 mm (Schedule 10S through Schedule 80S) |
| Coil Length per Spool | Standard: 10 m to 50 m; Custom: up to 200 m continuous |
| Coil Inner Diameter (Pack Diameter) | 150 mm to 600 mm (configurable per project requirement) |
| Surface Finish | 2B Annealed, No. 4 Brushed, or BA (Bright Annealed) per ASTM A270 |
| Tolerance — OD | ±0.10 mm (±0.004") |
| Tolerance — Wall Thickness | ±10% of nominal |
| End Condition | Plain cut, beveled, or pre-flared per customer specification |
| Applicable Standards | ASTM A269, ASTM A270, ASME B403.1, ISO 3506, EN 10217-7 |
| Heat Treatment | Solution Annealed at 1050–1150°C followed by water quench |
| Packaging | Wooden spool with moisture barrier film; desiccant included |
4. Manufacturing Process
The production of Series 794 coil tubes follows a rigorous multi-stage manufacturing workflow designed to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Procurement & Inspection: Hot-rolled stainless steel strip or seamless tube stock is sourced from certified mills. Incoming material undergoes spectroscopic analysis (OES) to verify chemical composition, along with visual and dimensional inspection per ASTM A270.
- Coil Forming / Bending: Straight tube sections are fed into a precision CNC coil forming machine. The forming die geometry is calculated to produce a consistent helical pitch without inducing plastic deformation, ovality, or residual stress in the tube cross-section. The bend radius is typically set at a minimum of 3× the tube OD to prevent kinking or wall thinning.
- Intermediate Annealing (if applicable): For tightly coiled configurations or thicker wall sections, a controlled solution anneal at 1050–1150°C relieves work-hardening and restores ductility. The tube is rapidly quenched to prevent sensitization (chromium carbide precipitation at grain boundaries).
- Precision Sizing & Calibration: Post-forming tube passes through a series of calibration rolls to restore and maintain the original circular cross-section, ensuring OD and wall thickness tolerances are met throughout the coil length.
- Surface Finishing: The coil tube receives the specified surface treatment — either mechanical polishing to achieve a 2B or No. 4 finish, or electrochemical pickling and passivation (ECP) to remove scale and establish a protective chromium oxide layer.
- Non-Destructive Testing (NDT): 100% visual inspection is performed. Helical ultrasonic testing (UT) or eddy current testing (ECT) is applied to detect internal laminations, cracks, or wall thinning. Hydrostatic pressure testing is conducted at 1.5× the maximum design pressure for a minimum of 30 seconds per ASTM A270.
- End Processing: Tube ends are cut to length, deburred, and optionally beveled to a 37.5° angle per ASME B16.25 for butt-welded connections.
- Final Inspection & Packaging: Dimensional verification, surface roughness measurement, and material certification documentation (Mill Test Reports / MTRs) are compiled. Coils are wrapped in protective film, secured on wooden spools, and labeled with traceability identifiers.
5. Applications
The Series 794 Stainless Steel Coil Tube is engineered for demanding thermal and fluid handling applications. Key deployment scenarios include:
- Fan Coil Units (FCUs): As documented in the referenced engineering analysis, stainless steel coil tubes are integral to the air-side heat exchangers within FCU systems. The coil tubes carry chilled water or hot water through serpentine passages, transferring thermal energy to or from air streams. The coil tube geometry maximizes surface area within a compact envelope, enabling efficient sensible and latent heat exchange.
- Chilled Water & Heating Loops: In central HVAC systems, coil tubes form the basis of plate-fin and tube-fin heat exchangers used in air handling units (AHUs), rooftop units (RTUs), and unitary cooling systems.
- Condensate Management: In FCU applications, condensate water — often containing dissolved chlorides, organic compounds, and microbial contaminants — continuously wets the coil tube surface. The corrosion resistance of 316L stainless steel prevents pitting, crevice corrosion, and biofilm-induced degradation, ensuring service life exceeding 25 years.
- Refrigeration Systems: Coil tubes are employed as evaporator and condenser elements in commercial refrigeration, cold storage, and industrial process cooling applications.
- Process Heat Exchangers: In chemical, pharmaceutical, and food processing industries, stainless steel coil tubes are used in double-pipe heat exchangers, spiral wound gaskets, and custom process coils where hygienic standards (FDA 21 CFR, 3-A Sanitary) are required.
- Automotive & Industrial Heaters: Coil tubes serve as heating elements in catalytic converters, exhaust heat recovery systems, and industrial process heaters.
- Geothermal & Solar Thermal Systems: The inherent formability of coil tubes enables their use in ground-loop heat exchangers and solar thermal collector manifolds.
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system ensuring that every Series 794 coil tube production lot meets or exceeds international standards:
| Certification / Standard | Scope of Compliance |
|---|---|
| ISO 9001:2015 | Quality Management System — Design, Manufacturing, and Delivery |
| ISO 14001:2015 | Environmental Management System |
| ISO 45001:2018 | Occupational Health and Safety Management System |
| CE Marking (EU) | Compliance with European Pressure Equipment Directive (PED 2014/68/EU) |
| EN 10204 3.1 | Inspection Documents — Material Test Reports per lot |
| Mill Test Reports (MTRs) | Chemical composition, mechanical properties, and heat treatment records for each production heat |
| NACE SP0169 | Guidelines for Control of Internal Corrosion in Oil and Gas Production Systems (where applicable) |
| RoHS & REACH | Restriction of Hazardous Substances and Chemical Regulation compliance |
7. Unique Selling Points
- Superior Corrosion Resistance: Austenitic stainless steel construction eliminates the need for internal coatings or galvanic protection, providing a service life 3–5× longer than carbon steel alternatives in condensate-laden FCU environments.
- Continuous Coil Configuration: Eliminates field welding joints, reducing potential leak points and installation labor by up to 40% compared to straight tube segments requiring on-site butt welding and post-weld passivation.
- Customizable Geometry: Coil pitch, pack diameter, and tube dimensions are tailored to specific heat exchanger designs, enabling optimal airflow distribution and thermal performance within FCU and AHU packages.
- Full Traceability: Each coil spool is assigned a unique batch identifier linked to mill test reports, NDT records, and dimensional inspection data, ensuring complete supply chain traceability per ISO 9001 requirements.
- Hygienic Surface Quality: Available in electropolished (Ra ≤ 0.4 µm) finish for pharmaceutical, food-grade, and medical HVAC applications where microbial adhesion must be minimized.
- Engineering Support: Wenzhou Jixing provides application engineering consultation for FCU coil design, including thermal performance simulation, pressure drop calculation, and material selection guidance based on operating fluid analysis.
8. Ordering Information
Customers should specify the following parameters when placing an order for Series 794 Stainless Steel Coil Tubes:
- Stainless steel grade (304, 316L, or alternative)
- Outer diameter (OD) and wall thickness (nominal and schedule)
- Required coil length and pack diameter
- Surface finish specification (2B, BA, No. 4, or electropolished)
- End condition (plain, beveled, flared, or threaded)
- Applicable standard(s) and required certifications
- Operating conditions (temperature, pressure, fluid type)
For technical inquiries, application engineering support, or sample requests, contact Wenzhou Jixing Metal Materials Co., Ltd. directly.